The present invention relates to a method for controlling incidences of combustion in an unloaded internal combustion engine of a vehicle.
An unloaded operating state of an internal combustion engine can be present, when, at the vehicle, no gear is engaged or the clutch is opened or the vehicle speed is equal to zero. In this context, it is possible for very high load dynamics and engine-speed dynamics to set in, when the unloaded engine is revving at almost no load. Because of these increased load dynamics and engine-speed dynamics, the engine is subject to a higher tendency for combustion knock in the unloaded operating state. However, this combustion knock during an unloaded operating state of an internal combustion engine, which is also referred to as no-load revving, is particularly disadvantageous because effective and reliable knock control is made more difficult by the increased dynamics (load dynamics and engine-speed dynamics) present. In addition, combustion knock especially has a disadvantageous effect on ride comfort during an unloaded operating state, because it is easy to detect acoustically, and it is annoying in this operating state.
The example method of the present invention for controlling incidences of combustion in an unloaded internal combustion engine of a vehicle is characterized by the following:
determining a load-dynamics threshold;
detecting an unloaded operating state of the internal combustion engine;
detecting the exceeding of the load-dynamics threshold in the unloaded operating state;
retarding the ignition timing to form a load-dynamics aiming-off allowance.
The occurrence of a majority of combustion-knock incidences caused by the increased load dynamics and engine-speed dynamics setting in the unloaded operating state may be prevented in a reliable and effective manner. Because of the increased tendency for combustion knock, the load-dynamics aiming-off allowance to be set in the unloaded operating state may be greater than the load dynamics and engine-speed dynamics triggered in loaded operation, i.e., when the gear is engaged and the clutch is closed. By determining a load-dynamics threshold, it is possible to reliably and precisely define an operating state having increased knock tendency. Unloaded operation of the internal combustion engine may be established as being when no gear is engaged or the clutch is opened (clutch pedal pressed down) or the vehicle speed is equal to zero. Therefore, it may be possible to quickly and reliably detect a so-called xe2x80x9ctip-inxe2x80x9d operating state, according to which the engine undergoes no-load or nearly no-load revving in the unloaded operating state, the probability of combustion knock occurring increasing due to the increased load dynamics and engine-speed dynamics simultaneously setting in. After detecting this operating situation, which may be critical with regard to the tendency for knock, it may be possible to prevent combustion knock in the engine or at least limit it to as few combustion incidences as possible, by producing a sufficient load-dynamics aiming-off allowance through corresponding retardation of the ignition timing.
The speed under load and the engine speed may be used as operating parameters for detecting an unloaded operating state of the engine and an engine-speed increase of the engine that is at least nearly without load. In particular, the speed under load and engine speed may present themselves as operating parameters for detecting a xe2x80x9ctip-inxe2x80x9d operating state, according to which no-load or nearly no-load revving of the engine occurs, possibly along with the load-dynamics threshold being exceeded, when the clutch is disengaged or a gear is not engaged or the vehicle speed is equal to zero. In this context, the speed under load and the engine speed may be ascertained in a simple and precise manner.
According to an exemplary embodiment, the ignition-timing retard value may be calculated from an ignition-retard value dependent on the engine speed. An ignition-retard value calculated as a function of the specific engine speed may be particularly suitable for ensuring a sufficient load-dynamics aiming-off allowance in a xe2x80x9ctip-inxe2x80x9d operating state.
According to another exemplary embodiment, the ignition-timing retard value may be calculated from the sum of an adaptive ignition-retard value and an ignition-retard value dependent on the engine speed. In this manner, the necessary load-dynamics aiming-off allowance may be calculated from an adaptive component and a component dependent on the engine speed. In this connection, the value of the adaptive load-dynamics aiming-off allowance may be known, while the value of the load-dynamics aiming-off allowance dependent on the engine speed may be determined as a function of the specific engine speed present in the unloaded operating state.
While the ignition timing is retarded, the adaptation of the knock-control dynamics may be deactivated. In particular, this allows the option of preventing the adaptation unit for the knock-control dynamics from unlearning the stored, adapted values ascertained for loaded operating states, especially due to the adjusted, engine-speed-dependent load-dynamics aiming-off allowance. This may allow the driveaway characteristics of the corresponding vehicle to be markedly improved after the unloaded operating state is brought to an end.
The ignition timing may be retarded below a predeterminable vehicle-speed threshold. In doing this, dynamic combustion knock, which may be relatively easy for a vehicle user to hear or detect, particularly at lower vehicle speeds, and therefore may have a negative effect on the ride comfort, may be prevented in the unloaded operating state of the engine.
The present invention may provide for the load-dynamics threshold being determined by a control device or stored in it; the unloaded operating state of the engine and the exceeding of the load-dynamics threshold in the unloaded operating state may be detected by a detection unit, and the ignition timing may be retarded by an ignition-timing adjustment unit to form a load-dynamics aiming-off allowance. This may allow at least a reduction in the combustion knock in a quick and reliable manner, during a xe2x80x9ctip-inxe2x80x9d operating state of the internal combustion engine.
Additional embodiments of the present invention may be derived from the description.